CSD is an ex-situ materials growth technique where chemical solutions are first prepared using inorganic or metalorganic metal salts which are dissolved in either organic or water in stoichiometric ratios to be used as precursors for complex materials. These solutions are then deposited onto a substrate using any of the available methodologies (spin coating, dip coating, web coating, ink jet printing, etc.), depending on the size and characteristics of the desired material to be prepared. The film thickness can be easily controlled through selection of the salts concentration in the solutions and each deposition technique requires specific rheological properties. CSD can also be used to prepare self-assembled nanostructures using ultradiluted solutions while nanocomposite films are prepared, either using complex multicomponent solutions leading to spontaneous phase separation of immiscible crystalline phases, or using colloidal solutions with prepared nanoparticles. Stabilized solutions of nanoparticles can be prepared following different approaches, among them microwave reactors.
The first characteristics which need to be controlled therefore in CSD growth are the chemical purity, metal stoichiometric relationship of the metal ions, the solution stability and rheological properties of the solutions (viscosity, contact angle, surface tension), as well as nanoparticle size and solution stability in the case of colloidal solutions. DLS and TEM are useful tools to characterize the nanoparticle size in the solutions.
After film deposition, the solutions are dried and the chemical precursors pyrolyzed to lead to an amorphous or nanocrystalline porous solid with well-defined thickness. A wide range of thermal processes can be applied for this step, usually performed under well-defined controlled atmospheres and heating ramps. Specific furnaces need to be used and analytical tools allow correlating the decomposition process with the films microstructure. Film thickness can be carefully controlled through selection of solution and depositions parameters and it can be measured through optical interferometry, ellipsometry or profilometry. TGA-DTA, Evolved Gas Analysis (EGA), optical and electron microscopy, IR spectroscopy and X-ray diffraction are the most common tools to follow the film evolution during or after the thermal processes. TEM and cross section FIB images are also very useful to analyze the film homogeneity and final porosity.
The final step to achieve high quality films is a selected high temperature growth process which transforms intermediate phases into the final desired phase. Control of the nucleation and growth conditions will closely determine the final microstructure and functionality of the films. Different types of heating procedures have been used (conventional resistive heating, rapid thermal annealing, laser annealing) to prepare ferromagnetic, ferroelectric, multiferroic, metallic, semiconducting or superconducting materials.
The CEM Focused Microwave Synthesis System, Discover, is designed to enhance tha ability to perform chemical reactions under controlled conditions on a laboratory scale. The system facilitates either homogeneus or heterogeneus solution phase chemistry, solid phase chemistry or chemistry conducted on solid supports. It accommodates vessels ranging in working volume from 5ml to 125ml for reactions performed under atmospheric conditions and 10ml or 35ml vessels with septa in addition to 80ml vesselsfor reactions performed at elevated temperatures and pressures at elevated temperatures and pressures.
Microwave from Milestone
The main characteristic of this new microwave equipment is that it has several accessories to carry out a great variety of experiments. It is designed for liquid-liquid synthesis, solid-solid synthesis, and for digestion experiments.
FEATURES:
The equipment can work, basically, in three different configurations, all within the same platform:
Classic synthesis glassware: system at atmospheric pressure for chemical synthesis.
Synthesis at high-pressure: for chemical synhtesis and digestions at high temperature.
Synhtesis in solid-phase: for solid-solid reactions.
The microwave is equipped with many pressure and temperature (infrared and thermocouple) sensors, vapor sensors, stirring (0-400 rpm).
XPS is a surface spectroscopic technique for quantitative measurements of the elemental composition or stoichiometry and the chemical state of the present elements, like their oxidation state and chemical bonds. XPS is highly surface sensitive, giving chemical and binding energy information from the a narrow region close to the surface.
XRD provides non-destructive information on the structural order of a material. At large scattering angles XRD permits to identify different crystal phases and to quantify lattice distances and crystalline volume fractions. At low angles of incidence the surface roughness of a single crystal and the thickness of a deposition layer can be obtained.
PL is a non-contact, non-destructive method of probing the electronic structure of materials, often used in the context of semiconductor devices to determine the bandgap energy, the composition of heterostructures, the impurity levels, the crystal quality, and to investigate recombination mechanisms.
NR is dedicated to the study of interfaces. The reflected intensity at grazing angle of a non polarized white neutron beam is measured as a function of wavelength. The variation of reflectivity is linked to the concentration profile perpendicular to the interface. Thickness (1-500nm), composition and roughness (1-20nm) of each layer are determined.
Surface plasmon resonance instruments enable to measure in real time the biomolecules binding onto the sensing surface by monitoring the induced plasmonic resonance peak shift at the gold-liquid interface. This technique allows real-time detection and monitoring of biomolecular binding events.